Dynatron oscillator circuit



Patented Jan. 12, 1937 PATENT OFFICE DYNATRON OSCILLATOR CIRCUIT JamesN. Whitaker, Tuckahoe, N. Y., assignor to Radio Corporation of America,a corporation of Delaware Application March 1,

5 Claims.

This invention relates to electron discharge device oscillator circuitswhich are adapted to generate energy at frequencies which bearpredetermined relationships with respect to the 5 frequency of theapplied energy.

An object of the present invention is to provide a simplified and highlyeiiicient oscillator circuit arrangement for generating a substantiallypure sinusoidal wave free from distortion.

Another object is to provide such an arrangement whereby there may beobtained with a high degree of accuracy any desired multiple orsub-multiple of a predetermined frequency.

Heretofore in the communication field, there have been used for thegeneration of harmonic frequencies, both audible and inaudible, suchapparatus as multivibrators, Gulstadt relays, and over-loaded vacuumtubes. These frequency generators have been found to be highly unstable,and are known to produce waves which are so distorted as to be incapableof use in many circuit arrangements without the employment of additionalapparatus, a matter which usually increases the cost of the system andinvolves the use of unnecessarily complicated circuits. A furtherdisadvantage of these latter arrangements is the difficulty of obtainingsatisfactory control of the system at the remote harmonics orsub-harmonics of the fundamental frequency.

The foregoing disadvantages, however, are overcome in accordance withthe present invention which provides a simple and highly stable dynatronoscillator system capable of generating substantially pure sinusoidalwaves of any desired harmonic or sub-harmonic of the fundamentalfrequency. By means of the present invention there is obtained adynatron oscillator which is very desirable, not only from thestandpoint of accuracy, dependability, maintenance and cost ofconstruction, but also for the ease with which the different frequenciesmay be selected.

The accompanying drawing is a preferred embodiment of the invention andis given merely by way of example to illustrate the principles of theinvention. Referring to this drawing in more detail, there are shown aplurality of dynatron oscillator circuits in cascade comprising screengrid electron discharge devices I and 2 with which there is associatedin the input circut a control or fundamental frequency apparatus 3having any desired high or low frequency, and to the output circuit ofwhich there may be coupled any desired utilization means, such as .anamplifier. y

1933, Serial No. 659,111

(Cl. Z50-36) Control frequency apparatus 3 may comprise a tuning forkoscillator or any other suitable means and is coupled by means oftransformer 4 to the grid 5 of the tube I, negative bias for which maybe applied in any desired manner. The anode 9 of tube I is connected tothe high potential side of a tunable, parallel connected, resonant tankcircuit comprising an inductance 'I and a variable condenser 8. Thescreen grid Ii! of the tube is arranged to have a higher positivepotential than the anode with respect to the cathode.

Coupled to the anode circuit of tube I in cascade relationship is thegrid of screen grid tube 2 whose elements are arranged in a manner iden-L tical with tube I. A similar tunable output tank circuit Il, I2 isprovided for this tube. Both dynatron oscillators I and 2 are designedto operate over a region where the anode resistance is negative, theindividual output circuits thereof being made to oscillate by utilizingthis negative anode resistance.

Separate voltage dividers I 4, I5 and I6, Il are used to supply theproper voltage to the respective anodes of each dynatron oscillator.This construction prevents interaction between tubes I and 2 andprovides the desired optimum voltage for each oscillator stage.

Similarly, since the tubes function most eciently as sub-harmonicproducers with a low bias, a voltage dividing arrangement I8, I9 may beused to reduce the controlling voltage.

In the operation of the system, the arrangement may be used either as afrequency multiplier or as a so-called frequency divider or subharmonicproducer, the frequency which is higher or lower than the fundamentalcontrolling frequency being obtained by varying condensers 8 and I2which change the resonance of the tunable oscillator tank circuits. Thefrequencies obtainable in each of these tank circuits may be any simplefraction of the controlling frequency.

Although in practice only one dynatron screen grid tube may be used, ithas been found desirable in order to obtain perfect control over arather wide range of variations to use two stages, as shown, bothoscillating at the same frequency. This is so because the voltages andvarious circuit constants required for perfect frequency control atremote sub-harmonics do not lend themselves readily to the production ofa desired sine wave output, and for this reason one stage, such as tubeI, may be used for such a purpose as dividing or multiplying thefrequency, and the other stage, tube 2, for producing the necessary sineWave output. Accordingly, both stages may be tuned to oscillate at thedesired output frequency, the first being stabilized by the controllingfrequency and the second stage being stabilized by the first. Since itis very easy to stabilize one of the circuits by feeding into it, at avery low amplitude, energy of a frequency very close to its outputfrequency, the tank circuit II, I2 in the last oscillator is arranged tohave a low L-C ratio. In the system just described, theI4 variablecondensers 8 and I2 are shown arranged for unicontrol operation, bothcondensers being operated from a common shaft I3 in the drawing.

In order to obtain frequencies close together it has been found to beadvantageous to have one of the stages, such as oscillator I, act as amultiplier, while the other stage, that is, tube 2, acts as a divider.In this manner there is available twice as many frequencies, by firstmultiplying and then dividing, than can be obtained by simply dividingthe controlling or fundamental frequency. For example, if the fixedfrequency of the controlling apparatus 3 is 810 cycles, then the second,third, fourth and fifth,

etc. sub-harmonics will be 405, 270, 202.5 and 162, etc. cycles,respectively, and these are the only sub-harmonic frequencies at whichgood control canbe obtained. However, if it is desired to obtainfrequencies between the abovementioned frequencies the fundamentalfrequency of 810 cycles may be multiplied by tuning the output circuitof stage I to 1620 cycles, and energy of the latter frequency fed intooscillator circuit 2 from whose output circuit I I, I2 there may then beObtained the second, third, fourth, fth, sixth, seventh, eighth, andninth, etc. rsub-harmonics of the impressed 1620 cycles which will be810, 540, 405, 324, 270, 231.4, 202.5, 180, etc., respectively. In thislatter arrangement, of course, it will not be desired to use unicontrolmeans between condensers 8 and I2, although such manner of control maybe useful between condenser I2 and the output circuit of a succeedingstage.

By exercising great care in adjusting the resonant circuits and platevoltages in the vpresent invention it has been found that any desiredremote harmonic or sub-harmonic of the control frequency may be obtainedwith no difficulty whatsoever. In a particular embodiment used nodifficulty was experienced in obtaining frequencies down to 30 cyclesand even lower from an 810 or 1620 cycle frequency control.

Although the system of the present invention has been describedhereinabove in connection with audible frequencies, it should bedistinctly understood that it is not limited thereto since' theprinciples may be applied equally as well to. high radio frequencieswell above the audible range.

The present invention has been found to be especially useful forgenerating a tone which may act as a carrier on a line for facsimile orother high frequency keying systems where both the keying frequency andthe line tone are synchronized by a common frequency standard, althoughit will be evident that it may be utilized in various otherorganizations wherever there is need for any oscillator circuit.

I claim:

1. A harmonic generator comprising a first dynatron oscillator circuitand a second dynatron oscillator circuit, each of said dynatron circuitsas indicated comprising an electron discharge device having anode,cathode, screen grid and control electrodes, means for applying to theanode, cathode and screen grid of each of said devices potentials ofsuch values that each device has a negative resistance between itscathode and anode, an input circuit connected between the controlelectrode and cathode and providing a source ofV controlling frequencyfor said first device, an output circuit coupled to the anode of eachden vice comprising a resonant tank circuit, each tank circuitcomprising a reactor of such value that its associated output circuit istuned to a frequency different from said controlling frequency and suchthat the quotient of the larger of the two frequencies divided by thesmaller of the two frequencies is an integer, and means for coupling theoutput circuit of the yrst device to the control electrode of the seconddevice.

2. A harmonic generator comprising a first dynatron oscillator circuitand a second dynatron cathode and screen grid of each of said devicesVVpotentials of such values that each device has a negative resistancebetween its cathode and anode, the potentials applied to said screengrids having higher positive values than those appliedr to theirassociated anodes, an input circuit 'connected between the controlelectrode and cathode Y and providing a source of controlling frequencyfor said first device, an output circuit coupled to the anode of eachdevice comprising a resonant tank circuit, each tank circuit comprisinga reactor of such value that its associated output circuit is tuned to afrequency different from said controlling frequency and such that thequotient of the larger of the two frequencies divided by thesmaller ofthe two frequencies is an integer, and means for coupling the outputcircuit of the first device to the control grid of the second device.

3. A harmonic generator comprising a first dynatron oscillator circuitand a second dynatron oscillator circuit, each of said dynatron circuitscomprising an electron discharge'device having anode, cathode, screengrid and control electrodes, means for applying to the anode, cathodeand screen grid of each of said devices potentials of such values thateach device has a negative resistance between its cathode and anode, aninput circuit connected between the control electrode and cathode andproviding Va source of controlling frequency for said first device, anoutput circuit coupled to the anode of each device, means whereby theoutput circuit of said first electron discharge device is tuned to amultiple of the controlling frequency, means for coupling the outputcircuit of the firstV electron discharge device to the control electrodeof the second electron discharge device, means whereby the outputcircuit of said second electron discharge device is tuned to asub-multiple of the frequency impressed on said device by said firstdevice, and circuit connections utilizing the energy from said lastoutput circuit.

4. A harmonic generator comprising a first dynatron oscillator circuitand a second dynatron oscillator circuit, each of said dynatron circuitscomprising an electron discharge device having anode, cathode, screengrid and control electrodes, means for applying to the anode, cathodeand screen grid of each of said devices potentials of such values thateach device has a negative resistance between its cathode and anode, aninput circuit connected between the control electrode and cathode andproviding a source of controlling frequency for said first device, anoutput circuit coupled to the anode of each device, means for couplingthe output circuit of the rst electron discharge device to the controlelectrode of the second electron discharge device, means whereby theoutput circuit of said first device is tuned to a sub-multiple of thecontrolling frequency, means whereby the output circuit of said seconddevice is tuned to a multiple of the frequency impressed on said device,and circuit connections for utilizing the energy from said last outputcircuit.

5. High frequency apparatus having, in combination, a multi-electrodeelectron discharge device dynatron oscillator comprising a cathode,anode, control electrode and auxiliary electrode, a source ofcontrolling frequency coupled to said control electrode for impressingthereon a voltage of a predetermined frequency, means for maintainingsaid control electrode at a potential which is relatively negative withrespect to the cathode thereof, means for maintaining said auxiliaryelectrode at a positive potential higher than said anode, a paralleltuned circuit comprising an inductance and a variable condenser incircuit with the anode of said oscillator, another similarmulti-electrode electron discharge' device dynatron oscillator whosecontrol grid is coupled to the anode of said first device, said paralleltuned circuit of said first device being tuned to a frequency which isdifferent from the predetermined frequency of said source of controllingfrequency and such that the quotient of the larger of the twofrequencies divided by the smaller of the two frequencies is an integer,and said parallel tuned circuit of said second device being tuned to afrequency which bears a harmonic relationship to the frequency of saidlast parallel tuned circuit.

JAMES N. WHITAKER.

